largest known emission nebula in terms of angular diameter as seen from Earth, extending about 35° in the southern constellations Puppis and Vela. A complex of diffuse, glowing gas too faint to be seen with the unaided eye, it was discovered by the Australian-born astrophysicist Colin S. Gum, who published his findings in 1955. The Gum Nebula lies roughly 1,000 light-years from the Earth and may be the remnant of an ancient supernova—i.e., violently exploding star.